Synthesis of Silicon Carbide Films from Partially Oxidized Polyvinylsilane by Carbon Tetrachloride Solution Casting
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Masayoshi Itoh Fukushima National College of Technology, 30 Aza Nagao, Taira Kamiarakawa, Iwaki, Fukushima 970-8034, Japan
Thomas Apple, Kevin V. Moraes, and Leonard V. Interrante Department of Chemistry, Rensselaer Polytechnic Institute, Troy, New York 12180-3590
Polyvinylsilane (PVS), derived from vinylsilane by radical polymerization, was partially oxidized in hot carbon tetrachloride solution by flowing air. If the air flow time is adjusted, soft gel films can be formed in a Teflon dish by casting the PVS solution. After the PVS films were peeled from the substrates, they were pyrolyzed at various temperatures. Spectroscopic studies of the pyrolyzed films up to 1273 K suggested that carbosilane (Si–CH2–Si) structures are formed in the films at 473–673 K. The compositions of the amorphous films obtained at 1673 K were approximately SiC1.38O0.21 and SiC1.41O0.51, depending on the crosslinking conditions. The oxygen incorporated in the films was removed in the form of CO and SiO during further heating at 1673–1873 K. The compositions of the films were changed to approximately SiC1.25 and SiC1.26, respectively, at 2073 K. The films obtained at 1273 K did not show degradation during the oxidation at 1273–1673 K while a protective silica layer was formed on their surfaces.
I. INTRODUCTION
Polymer precursor methods constitute a unique process for the synthesis of covalently bonded ceramic materials with special forms that are normally difficult to obtain by conventional powder processing methods. Synthesis of silicon carbide fibers from polycarbosilane (PCS) is the earliest and most typical case.1–4 Various types of silicon carbide fibers with improved hightemperature stability are now commercially available.5–8 The use of organosilicon precursors as a matrix source in fabricating ceramic matrix composites (CMC) has also been pursued.9–12 The precursor method also possesses potential application for coatings, foams, and functional porous materials. Such processability is based on the viscoelastic nature of the precursor polymers. We studied polyvinylsilane (PVS), synthesized by radical polymerization of vinylsilane for silicon carbide precursor uses. With polymerization catalyst, 2,2azobis(isobuthyronitrile) (AIBN) at about 70 °C, polymer chains composed of 50% –CH2–CH(SiH3)– units and 50% –CH2–CH2–SiH2– remainder units are obtained.13,14 The prepared PVS is a viscous liquid at room a)
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J. Mater. Res., Vol. 17, No. 1, Jan 2002 Downloaded: 18 Mar 2015
temperature and is perfectly compatible with polycarbosilane (PCS). A blend of PVS and PCS has been shown to be effective in improving the spinnability of the precursor melt (473–573 K) when thin SiC fibers are created.15,16 The liquid nature of PVS is also favorable in CMC production for impregnating the precursors into the reinforcement fiber fabrics.17 However, the most attractive point of PVS is its stability to oxygen and humidity at room temperature,
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